Oxy-fuel gas cutting torches are commonly used for cutting ferrous alloys and some non-ferrous metals, as cuts can be effected through very thick billets. In operation, an oxy-fuel torch directs an ignited stream of oxygen and fuel gas onto the surface of the metal to be cut. The metal is thus heated to its ignition temperature, at which point a stream of cutting oxygen directed at the surface oxidizes the heated metal to effect the cut.
The cutting torch may be one of a premixed or a postmixed type torch. In a premixed torch, preheat oxygen and fuel gas are mixed within the torch head before being discharged for ignition. In a postmixed cutting torch, the preheat oxygen and fuel gas are discharged from the torch in unmixed streams. Turbulence in the discharged streams mixes the oxygen and fuel gas before ignition occurs. A principal advantage of the postmixed cutting torch is that it is not subject to flashback, a potential hazard associated with the use of premixed torches. Flashback occurs when the oxygen and fuel gas mixture in a premixed torch ignites within the torch head. Postmixed torches are therefore commonly employed for heavy industrial applications where a torch is subjected to considerable heat. A further advantage of the postmixed torch is that postmixed nozzles produce a longer and wider heat zone than premixed nozzles. This permits the postmixed torch to operate farther from the work, decreasing the heat stress on the torch and increasing the service life of the nozzle.
Many prior art postmixed nozzles for oxy-fuel gas torches operate in substantially the same way. A stream of cutting oxygen is discharged from an axial bore in the nozzle. A plurality of fuel gas discharge orifices arranged in a concentric ring around the axial bore discharge preheat fuel gas and a second plurality of gas discharge orifices arranged in an outer concentric ring discharge preheat oxygen which acts as an envelope that surrounds the fuel gas stream. As the gas streams flow toward the workpiece, a mixing of the fuel gas and the oxygen occurs and the mixture ignites to heat the workpiece.
An example of a prior art postmixed oxy-fuel gas cutting torch and nozzle is taught in the U.S. Pat. No. 6,277,323 which issued to Bissonnette on Aug. 21, 2001. That patent describes a combination cutting torch and nozzle assembly for postmixed oxy-fuel cutting using an annular streams of preheat oxygen gas surrounding a fuel gas stream. The nozzle assembly is secured to the head of the cutting torch by a hollow retaining nut which forms an annular gap with the nozzle assembly for discharging the outer preheat oxygen gas stream. The preheat oxygen gas is connected to a pure oxygen source (e.g., 99%+purity), and therefore discharges a sizable volume of pure oxygen during operation, to ensure a high flame temperature. Hence, pure oxygen consumption is an important cost factor in the operation of postmixed oxy-fuel gas cutting torches.